1. Field of the Invention
The present invention relates to semiconductor device fabrication.
2. Description of the Related Art
Some modern semiconductor device fabrication procedures utilize multiple process gas compositions where in-process changes between different applied process gas compositions are required to be made quickly and accurately. Rapid process gas composition switching is an operation performed during a semiconductor device fabrication procedure in which the flow of process gas compositions into a process module, e.g., into a plasma processing chamber, is changed with high timing precision. Rapid process gas switching can require changing of the process gas composition delivered to the process module within a time period of less than about 1 second, and in some cases even within a time period of less than about 0.1 second. The process gas composition switching time should be accurate in comparison with a clock, and in some cases in accordance with a processing recipe. For example, if a processing recipe indicates that a particular process gas composition transition should occur 20 seconds into the processing recipe (or at a nominal step transition time), the process gas composition transition should occur between 19.9 seconds and 20.1 seconds into the processing recipe. Most semiconductor device fabrication systems are not able to approach this level of timing precision with regard to process gas composition transition. It is within this context that the present invention arises.